JPH03224692A - Treatment of waste water from methacrylic acid producing plant - Google Patents

Abstract

PURPOSE:To efficiently treat waste water contg. acetic acid and aldehydes from a methacrylic acid producing plant by wet-oxidizing the org. substances in the waste water with fed gas contg. molecular oxygen at a specified temp. under a specified pressure. CONSTITUTION:Waste water contg. acetic acid and aldehydes sent from a methacrylic acid producing plant to a line 13 is sent to a heat exchanger 5, preheated and fed into a wet oxidation reactor 1 packed with a solid catalyst. Gas contg. molecular oxygen fed from a line 14 is compressed with a compressor 6 and fed into reaction tubes 11 in the reactor 1 through a line 19. In the reactor 1, the org. substances in the waste water are wet oxidized with the fed gas at <=370 deg.C under the pressure required to maintain the liq. phase of the waste water.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for purifying methacrylic acid production plant wastewater by wet oxidation in the presence of a solid catalyst. Specifically, the present invention involves treating wastewater from a methacrylic acid production plant by gas-phase catalytic oxidation of isobutylene and/or t-butyl alcohol containing acetic acid and aldehydes in the presence of a solid catalyst to eliminate these organic substances in the wastewater. This invention relates to a method for purifying wastewater by converting most of these organic substances into harmless carbon dioxide, water, etc. by wet oxidation while supplying a gas containing molecular oxygen. The present invention also relates to a method for producing methacrylic acid incorporating the above wastewater purification process.

(Prior art) In general, methods for treating wastewater from methacrylic acid production plants include:
Activated sludge method and direct combustion method are known.

As is well known, the activated sludge method requires a long time to decompose organic matter, and it is also necessary to dilute the wastewater to a concentration suitable for the production of algae and bacteria, so the activated sludge treatment facility requires a large area. There are drawbacks to it. In particular, when methacrylic acid production plant wastewater is treated using the activated sludge method, the wastewater contains aldehydes such as formaldehyde and acetaldehyde, which are pre-biotics, so it is necessary to dilute the wastewater at a high ratio. Furthermore, the treatment efficiency of activated sludge becomes unstable, resulting in high wastewater treatment costs and problems in that treatment is slow. Furthermore, the acetic acid contained in the wastewater is considered to be a substance with low biodegradation efficiency, but due to environmental regulations, it must be treated with a high degree of decomposition, but as mentioned above, the activated sludge method has problems. are doing.

On the other hand, when the direct combustion method is applied to wastewater from a methacrylic acid production plant, a large amount of combustion aid is required due to the low concentration of organic matter in the wastewater, resulting in high treatment costs. Furthermore, since this wastewater is mainly composed of low-boiling organic substances, it is difficult to concentrate it as a pretreatment.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a method for efficiently treating methacrylic acid manufacturing plant wastewater containing acetic acid and aldehydes over a long period of time.

Another object of the present invention is to provide a method for treating wastewater which has the advantage that treated water can be reused as water for a methacrylic acid manufacturing plant.

Still another object of the present invention is to provide a novel method for producing methacrylic acid.

(Means for Solving the Problems) In summary, wastewater from a methacrylic acid production plant containing acetic acid and aldehydes is treated at a temperature of 370°C or less using a wet oxidation reactor filled with a solid catalyst. This is achieved by a method for purifying methacrylic acid production plant wastewater by wet oxidizing the organic substances in the wastewater under a pressure that maintains the liquid phase with the supply of a gas containing molecular oxygen.

These methods include gas phase catalytic oxidation of a raw material gas containing isobutylene and/or t-butyl alcohol;
The resulting oxidation gas is brought into contact with water and absorbed, and the wastewater containing acetic acid and aldehydes after separating methacrylic acid from the resulting aqueous solution is heated at 370°C using a wet oxidation reactor filled with a solid catalyst. The organic substances in the wastewater are purified by wet oxidation under the supply of a gas containing molecular oxygen at a temperature and a pressure such that the wastewater remains in a liquid phase; This can also be achieved by a method for producing methacrylic acid, which comprises circulating wastewater to an oxidation product gas absorption step to absorb the oxidation product gas.

(Function) According to the present invention, most of the organic substances such as acetic acid and aldehydes can be converted into harmless carbon dioxide gas, water, etc. by wet oxidation treatment of methacrylic acid production plant wastewater using a solid catalyst. It has become possible to complete a methacrylic acid manufacturing plant that does not generate waste.

As a wet oxidation method, the non-catalytic Zimmerman method has been known. Various methods have also been proposed in which various oxidation catalysts are used to speed up the reaction rate. However, this method has not yet been adopted as a wet oxidation treatment method for methacrylic acid production plant wastewater containing acetic acid and aldehydes.

The methacrylic acid production plant wastewater to be treated in the present invention contains acetic acid and formaldehyde, and is not particularly limited, but typically has the following composition, for example.

Acetic acid 0.01-20% by weight Acrylic acid 0.02-3% by weight Methacrylic acid
0.04-4% by weight Aldehydes 0.0
2 to 3% by weight Other organic substances 0 to 3% by weight Water The remainder Among wastewater from a methacrylic acid manufacturing plant, conventional wet oxidation methods have low treatment efficiency and require secondary and tertiary treatment, especially when it comes to decomposing acetic acid. However, by adopting the wet oxidation method using the catalyst of the present invention, it was found that the process could be performed more efficiently, and the equipment could also be made more compact, making it possible to reduce treatment costs. .

The supply of the gas containing molecular oxygen is preferably carried out at an actual gas linear velocity in the catalyst layer within a range of 0.6 to 20 cm/see, more preferably within a range of 1 to 12 cm/sec. Actual gas linear velocity is the gas flow rate under temperature and pressure in the catalyst layer, which is the cross-sectional area of the catalyst layer (plane perpendicular to the vertical axis).
It is divided by .

By keeping the actual gas linear velocity within this range, the gas can better agitate the gas and liquid in the catalyst layer, speeding up the dissolution of oxygen into the liquid phase and speeding up the desorption of carbon dioxide from the liquid phase.
The decomposition efficiency of acetic acid, which has poor reactivity, can be greatly improved. It also prevents an increase in pressure loss in the catalyst layer.In particular, when wastewater from a methacrylic acid production plant
In the case of wastewater containing 20% by weight and 0.02 to 4% by weight of aldehydes, the method of the present invention is preferably used because the reaction can be easily controlled and the wet oxidation can be carried out with good efficiency.

Furthermore, at a position 30% from the inlet side of the catalyst layer, 50 to 50% of aldehydes in the wastewater of a methacrylic acid production plant
By appropriately setting conditions such as reaction temperature, pressure, and liquid space velocity (LH3V) so that 100% of the acetic acid is oxidized, the removal efficiency of acetic acid, which is difficult to oxidize, at the outlet of the catalyst layer can be increased. This is because the temperature of the liquid is sufficiently raised due to the heat generated by the oxidation of the aldehydes, and the oxidation reaction of acetic acid is promoted.

In addition, oxidation of aldehydes occurs competitively on the catalyst active site, and the reduction in aldehydes promotes the oxidation of acetic acid.

In the present invention, the catalyst used is preferably an oxide containing titanium as a carrier.

Specifically, manganese, iron, cobalt,
Catalytically active elemental metals such as nickel, tungsten, copper, cerium, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium, or their compounds that are inert or sparingly soluble in water (e.g., oxides, chlorides, sulfides) etc)
is used.

The catalyst composition is 75 to 99.95% by weight of the carrier, preferably 85 to 99.9% by weight, and 25 to 0.05% by weight, preferably 15 to 0.05% of the metal or its compound as the catalyst active component element. It is in the range of 1% by weight. Preferably, among the catalytic active component elements, manganese, iron, cobalt,
Nickel, tungsten, copper, cerium and silver are used in amounts of 0 to 15% by weight as compounds, and platinum, palladium, rhodium, ruthenium and iridium are used in amounts of 0 to 5% by weight as metals, especially 0 to 3% by weight ( However, the total amount of both is 0.1 to 15% by weight). Among these, at least one metal selected from the group consisting of platinum, palladium, rhodium and ruthenium is added at 0.1
More preferred is a catalyst supported at ~5% by weight, especially 0.1-3% by weight.

Furthermore, a catalyst in which the above-mentioned platinum group metal is supported on a titania-zirconia carrier is preferable. In particular, in this catalyst 20-90 mol% titania and 8 mol% zirconia
When a binary composite oxide consisting of 0 to 10% is used, it has excellent activity, hot water resistance, acid resistance, and durability, so it can be used to treat wastewater from a methacrylic acid manufacturing plant containing aldehydes and acetic acid. Are better.

Moreover, as for the shape, any of pellet-like, spherical, honeycomb-like, ring-like shapes, etc. can be adopted.

Various types of reactors can be used in the present invention, such as an adiabatic single-tube cylindrical reactor and a reactor with a heat exchange function, but it is better to use a reactor with a heat exchange function. More preferred.

In conventional wet oxidation methods, a single-tube cylindrical reactor without heat exchange function is often used, and using this type of reactor takes into account the removal of reaction heat generated during wastewater decomposition. Therefore, it is not possible to treat highly concentrated wastewater. The methacrylic acid manufacturing plant wastewater targeted by the present invention also has a concentration of 0.0. It varies over a wide range from 1 to 20%, and when high-concentration wastewater is actually supplied, the calorific value increases (becomes).
The temperature of the liquid in the reaction tower rises significantly, and all of the water moves into the gas phase, making it impossible to react. In this case, the calorific value must be controlled by diluting the wastewater, which is undesirable because it increases the processing time.

Therefore, excellent effects can be obtained by using a heat exchanger type reactor as a reactor having a structure that allows sufficient removal of reaction heat.

By using this heat exchange reactor, heat is sufficiently removed from high concentration methacrylic acid production plant wastewater, so it can be easily treated without applying excessive pressure. Even when the calorific value is small, it is no longer necessary to excessively increase the reaction pressure in consideration of the rise in liquid temperature due to heat generation.In addition, cooling is performed according to the temperature and volume of wastewater from a methacrylic acid production plant. The amount of heat removed can be increased or decreased by adjusting the amount of heat transfer medium in the heat exchanger.
Can be controlled.

Furthermore, the reaction heat recovered in the reactor can be recovered as steam using the above-mentioned generation boiler via a heat transfer medium, or the heat can be effectively recovered for preheating waste water, etc., which reduces the operating cost and equipment cost of the device. etc. can significantly reduce costs.

Among these heat exchange type reactors, a multi-tubular cylindrical heat exchanger type reactor is preferred. This type simplifies the reactor model, making it easier to design and maintain, and reducing the use of highly corrosive materials by passing wastewater only through the inner tube, reducing reactor costs. (See Figure 1).

Furthermore, in the method of the present invention, a multi-tubular cylindrical heat exchanger type reactor having a gas supply device equipped with a gas supply nozzle at the bottom of each reaction tube (inner tube) is used, and the pressure loss of each gas supply nozzle is is 0.05 kg/C♂ or more, especially 0.1 to 1
Preferably, it is kg/cI#. Here, the pressure loss of each gas supply nozzle refers to the differential pressure that occurs under gas flow from the gas supply branch to each nozzle to the nozzle outlet.

Examples of the molecular oxygen-containing gas include air, pure oxygen, oxygen-enriched air, and the like.

According to the present invention, the multi-tubular heat exchanger type reactor can supply an equal amount of molecular oxygen-containing gas to each reaction tube by providing a gas supply nozzle at the bottom of each reaction tube. Moreover, this makes it possible to supply equal amounts of waste water to each reaction tube along with the gas generated from each gas supply nozzle. In order to supply the same amount of gas from the gas supply nozzle to each reaction tube, the pressure loss of each nozzle is
0.05kg/cIf! Above, above, preferably 0.05
~2kg/cIl? , more preferably 0. 1~1k
g/cI#.

This is 0. If the pressure loss is less than 0.5kg/c♂, there will be a difference in the gas flow rate supplied from each nozzle, resulting in a large drift, and as a result, it will be difficult to supply the same amount of gas to each reaction tube. be.

Furthermore, the difference in pressure loss between the plurality of nozzles of the gas supply device in the present invention is within 40%, preferably within 25%. If the difference in pressure loss between the nozzles exceeds 40%, it becomes difficult to supply equal amounts of gas to each reaction tube, and as a result, equal amounts of wastewater are not entrained, resulting in uneven flow of both gas and wastewater. This tends to occur, leading to a decrease in processing efficiency.

The nozzle type of the gas supply device of the present invention may have a structure that can generate a differential pressure, and gas can be supplied to the nozzle of the gas supply device using radial piping, ring-shaped piping, or a small air reservoir drum. (See Figure 3).

In the present invention, even better effects can be obtained by performing wet oxidation using a multi-tube cylindrical heat exchanger type reactor in the first stage and a single-tube cylindrical reactor in the second stage.

This is because we have found that in the wet oxidation reaction of the present invention, most of the reaction occurs near the inlet of the reactor, and the generation of reaction heat is also concentrated in this area. . That is, a reactor with a heat exchange function is used to remove heat only from the part necessary for removing the reaction heat, and then the remaining wastewater with a small calorific value discharged from the heat exchanger type reactor is passed through two stages. By introducing the reactor into a single-tube cylindrical reactor that does not have a heat exchange function, the remaining reactions were attempted to proceed adiabatically. By adopting such a configuration, the multi-tubular cylindrical heat exchanger type reactor can be downsized, so that the cost of the device, equipment cost, etc. can be reduced (see FIG. 2).

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of an apparatus for treating wastewater from a methacrylic acid production plant according to the present invention. First, line 13 from the methacrylic acid production plant.
The wastewater sent is sent to the heat exchanger 5 by the wastewater supply pump 7 and is preheated, and then supplied to the reactor 1. This reactor 1 has a plurality of inner tubes built into a body 12, and a dispersion plate (not shown) is provided at the bottom of the reaction tube, if necessary. On the other hand, the molecular oxygen-containing gas supplied from the line 14 is pressurized by the compressor 6, and then passes through the line 19 to the reaction tube 11 in the reactor 1.
supplied to Alternatively, the pressurized molecular oxygen-containing gas may be fed to the heat exchanger 5 along with the waste water via line 20, or a portion of the pressurized molecular oxygen-containing gas may be passed via line 19 and the remainder via line 20. It may also be supplied to the reactor 11 via the reactor 11.

A heat transfer medium is supplied to the outside of the inner tube (reaction tube) 11 in the reactor 1 through a line 15 by a circulation pump 3 to remove reaction heat generated during the reaction, and then discharged through a line 16. In the heat exchanger 4, cooling water supplied from the line 17 cools the heat transfer medium and recovers the heat of reaction. The wastewater treated in the reactor 1 is discharged through a line 18, cooled in a heat exchanger 5, and then supplied to a gas-liquid separator 8, where it is separated into harmless gas and water. In this gas-liquid separator 8, a liquid level controller LC detects the liquid level and operates a liquid level control valve 9 to maintain a constant liquid level, and a pressure controller PC detects pressure and operates a pressure control valve 9. 10 to maintain a constant pressure. Furthermore, the water to be treated extracted from the line 21 through the liquid level control valve 9 can also be used as water for methacrylic acid absorption in a methacrylic acid absorption tower of a methacrylic acid production plant.

FIG. 2 is a schematic diagram showing another embodiment of the present invention,
A multi-tube cylindrical heat exchanger type reactor is used in the first stage, and a single-tube cylindrical reactor is used in the second stage. The first heat exchanger type reactor 21a is the same as that shown in FIG. It is covered with material 42.

First, wastewater from the methacrylic acid production plant sent from the line 33 is transferred to the heat exchanger 25 by the wastewater supply pump 27.
After being preheated, it is supplied to the first reactor 21a. On the other hand, the molecular oxygen-containing gas supplied from the line 24 is pressurized by the compressor 26 and then supplied into the reaction tube 31 of the first reactor 21a via the line 40. Alternatively, the pressurized molecular oxygen-containing gas may be supplied to the heat exchanger 25 along with the waste water via line 39, or a portion of the pressurized molecular oxygen-containing gas may be transferred via line 39 and the remainder to the heat exchanger 25 via line 40. It may be supplied to one reactor 21a.

A heat transfer medium is supplied from the circulation pump 23 to the outside of the inner tube (reaction tube) 31 of the first reactor 21a through the line 35 to remove reaction heat generated during the reaction, and then to the line 36.
In the heat exchanger 44, the heat transfer medium is cooled and the reaction heat is recovered by cooling water supplied from the line 37. The wastewater treated in the first reactor 21a is then supplied to the second reactor 21b for treatment, then discharged from the wastewater line 38, cooled in the heat exchanger 25, and then passed through the gas-liquid separator. 28 where it is separated into harmless gas and water. In this gas-liquid separator 28, the liquid level is detected by the liquid level controller LC and the liquid level control valve 2
9 is operated to maintain a constant liquid level, and a pressure controller PC detects the pressure and operates a pressure control valve 30 to maintain a constant pressure.

Furthermore, the water to be treated extracted from the line 41 through the liquid level control valve 29 can also be used as water for methacrylic acid absorption in a methacrylic acid absorption tower of a methacrylic acid production plant.

FIG. 3 shows a multi-tubular cylindrical heat exchanger 49 used in the present invention.
1 is a diagram illustrating one embodiment of the invention. That is, each reaction tube 51 of the multitubular cylindrical heat exchanger 49 is filled with a solid catalyst, and methacrylic acid production plant wastewater is supplied to this reactor 49 from a line 53. On the other hand, molecular oxygen-containing gas is supplied from line 59 through each nozzle 60 . A heat transfer medium is supplied to the outside of the reaction tube 51 of this reactor 49 by a circulation pump 48, used for cooling the reactor, is discharged from a line 55, and is supplied from a line 57 to a heat exchanger 54. Heat recovery is performed by cooling water.

FIG. 4 is a schematic diagram showing still another embodiment of the present invention. That is, in the apparatus shown in Fig. 1, a single tube cylindrical reactor 61 is used instead of the multi-tube cylindrical heat exchanger type reactor, and the reaction heat recovery device is omitted. The same is true. In addition, in FIG. 4, members with 60 added to the reference numerals of each member in FIG. 1 represent the same members.

FIG. 5 is a flow sheet showing an outline of a method for producing methacrylic acid incorporating a wet oxidation wastewater treatment step. That is, the reaction product gas obtained by catalytic gas phase oxidation of isobutylene and/or t-butyl alcohol with a molecular oxygen-containing gas is sent from line 111 to methacrylic acid condensation column 1.
21 will be introduced. In this methacrylic acid condensation tower 121, the gas is rapidly cooled and condensed, and most of the methacrylic acid and acetic acid become an aqueous solution here. Further, the uncondensed portion is absorbed and collected by cooled absorption water containing a polymerization inhibitor supplied from the line 112 at the upper part of the condensing group 121, and taken out as a methacrylic acid aqueous solution from the lower part of the condensing group 121 through the line 113. . From the top of the condensing group 121, waste gas is discharged via line 114.

The aqueous methacrylic acid solution taken out from line 113 is led to the upper part of methacrylic acid extraction tower 122, while the solvent for extracting methacrylic acid oil is passed through line 128 to the upper part of extraction tower 122.
The methacrylic acid is supplied from the lower part of the line 116, and the two are brought into countercurrent contact in the extraction column 122, and the methacrylic acid is extracted into the solvent phase.
The aqueous phase is drawn off via line 117. The solvent phase after extraction is distilled in a solvent separation column 124,
The solvent is separated and recovered and recycled to the methacrylic acid extraction column 122 for use. On the other hand, crude methacrylic acid is extracted through line 115 and is made into a product through a methacrylic acid rectification step (not shown).

On the other hand, the aqueous phase after methacrylic acid extraction is led to a solvent recovery column 123 through a line 117 and distilled, and the solvent is supplied to a methacrylic acid extraction column 122 via lines 119 and 128. is taken out from the bottom of the solvent recovery column 123 via the reline 120, and a portion of this liquid is transferred via the line 125 to the methacrylic condensation group 1.
21 for reuse as absorption water, and the remainder is sent via line 13 to a wastewater wet oxidation process. In addition, the code|symbol 126 is a supply line of a polymerization inhibitor.

The wet oxidation process is the same as the process shown in FIG. Similarly, the steps shown in FIGS. 2 to 4 can be incorporated instead of the steps shown in FIG. 1. The wastewater treated in this step is circulated through line 127 to methacrylic acid condensation column 121 and used as absorption water.

By subjecting the wastewater discharged from this line 120 to wet oxidation using a solid catalyst, organic components in the wastewater are removed and purified. In this way, by purifying the wastewater in the solvent recovery tower 123 by wet oxidation, a closed and integrated method including wastewater treatment becomes possible as a method for producing methacrylic acid. In addition, since wastewater treatment can be performed in accordance with the amount and composition of wastewater that change due to fluctuations in operating load, it is easy to change the operation and conditions of the manufacturing method.

Furthermore, since the treated liquid purified by wet oxidation does not contain any substances that adversely affect the absorption of methacrylic acid, it can be reused as absorbed water in the methacrylic acid condensation column 121. As a result, the amount of water used can be significantly reduced, and the manufacturing cost of methacrylic acid can be reduced.

Next, the present invention will be explained in more detail by giving Examples.

Example 1 Wastewater from a methacrylic acid manufacturing plant was treated using the treatment apparatus shown in FIG. Reactor 1 has an inner diameter of 50 mm
, 20 reaction tubes (inner tubes) 11 with a length of 10 m are built into the body, and inside the reaction tubes 11 are 20 reaction tubes (inner tubes) with an average diameter of 5 mm and a length of 6 mm.
A pellet catalyst (PtO, 5% by weight supported on a titanium-zirconium composite oxide carrier) was packed so that the catalyst layer length was 8 m. Also, place an air distribution plate (
(not shown) was provided.

The methacrylic acid production plant wastewater sent from line 13 (the composition is shown in Table 1) is mixed with the air supplied from line 14, and the amount of wastewater passing through each reaction tube is 80 g/h.
r and air amount 20,80 ONg/hr (therefore, in the whole reactor, waste water amount 1.6 m3/hr and air amount 416
Nm3/hr, and the actual gas linear velocity is 7.4 cm/se
e) (line 19 Keizan) to reactor 1, and wet oxidation was carried out at a reaction temperature of 250° C. and a reaction pressure of 5 kg/coffG. Table 1 shows the composition and treatment efficiency of the water to be treated extracted from the line 21.

Table 1 Methacrylic acid plant wastewater treatment water treatment effect Acrylic acid 0.3 ND methacrylic acid 0.5 ND aldehydes 1.0
ND and others available! material
0.5. ND water
93.5 ND: Not detected 00 00 00 00 Example 2 In Example 1, the reactor type was changed to an adiabatic single-tube cylindrical reactor without heat exchange function (inner diameter 2
20mm, height 10m (however, the catalyst layer height is 8m), and the amount of waste water is 1. 2m3/hr.

Air volume 255Nm3/hr (via line 79),
Actual gas linear velocity 4. Table 2 shows the results of the same treatment except that the speed was 7 cm/see.

Example 3 In Example 2, the air amount was 264 Nm3/hr (via line 80) and the actual gas linear velocity was 4. 1. Same as above, except that the speed is 9 cm/sec. The results of the treatment are shown in Table 2.

Examples 4 to 6 In Example 1, the catalyst was changed to treat methacrylic acid production plant wastewater. Table 3 shows the catalyst composition and results at this time.

Table 3 Example 4 Example 5 Example 6 Catalyst composition Rh (0.6% by weight) Ru (1.5% by weight) Pd (1.5% by weight) -TZ -TZ
-TiO2 treatment efficiency (%) Acetic acid 99.4 96.0 91.0
Acrylic acid 100 10
0 100 methacrylic acid
ioo ioo
io.

Aldehydes 100 10
0 100 Other organic substances
100 99 9
8TZ: Titanium and zirconium composite oxide support (
Ti02/Zro2=60/40wt%) Ti0
2: Titania carrier Example 7 In Example 2, the reactor had an inner diameter of 70011110 N.
The height is 3 m, the catalyst layer height is 0.79 m, and the actual gas linear velocity is 0°4.
When the treatment was carried out in the same manner except that the velocity was changed to 6 cm/see, the treatment efficiency of acetic acid was 91%.

Example 8 In Example 1, the reactor had an inner diameter of 90 mm and a height of 12 m.
, six catalysts with a catalyst bed height of 8 m are used in series, and the actual gas linear velocity is 2
8. When the treatment was carried out in the same manner except that the rate was 1 cm/see, the treatment efficiency of acetic acid was 96.2%. However, the pressure loss in the catalyst layer increased significantly to 7 kg/cJ.

Example 9 In Example 2, the liquid was sampled at a position 30% from the entrance of the catalyst layer and the treatment efficiency was determined; acetic acid was 72%, methacrylic acid was 88%, and methacrylic acid was 86%.
%, aldehydes 98%, and other organic substances 8%
It was 5%.

(Effects of the Invention) In the present invention, since the methacrylic acid production plant wastewater is highly oxidized, the treated water can be reused as plant water. A plant for producing methacrylic acid by oxidation of isobutylene and/or t-butyl alcohol in a catalytic gas phase.
However, water is used throughout the equipment. In particular, large amounts of water are used in methacrylic acid absorption towers and distillation towers, and recirculating the treated water after wet oxidation leads to a significant reduction in utility costs and further reduces methacrylic acid production costs. Becomes cheaper.

The water to be treated after the wet oxidation of the methacrylic acid production plant wastewater of the present invention is characterized by containing a small amount of acetic acid in high throughput operation, but the present inventors believe that this can be used without affecting the methacrylic acid production plant. We have discovered that this is a wastewater treatment method that enables closed methacrylic acid production plants. This combination can enable a methacrylic acid production plant without wastewater discharge.

Conventionally, wastewater from methacrylic acid manufacturing plants has too high a concentration of organic substances to undergo activated sludge treatment, requiring high dilution.On the other hand, the concentration of organic substances is too low to perform combustion treatment, so auxiliary treatment is required. The problem was that it required a large amount of fuel. On the other hand, the wet oxidation method according to the present invention is an extremely suitable method for treating wastewater from a methacrylic acid production plant because it can directly and efficiently treat wastewater.

Furthermore, when the acetic acid concentration in the water absorbed by the methacrylic acid collector increases, the acetic acid concentration in the waste gas containing raw material gases such as unreacted olefins that is returned to the raw material system increases, which adversely affects the methacrylic acid production catalyst.

On the other hand, in the wet oxidation treatment according to the present invention, the water after treatment contains almost no acetic acid, so the production efficiency of methacrylic acid can be improved by circulating the water and using it as absorbed water.

[Brief explanation of drawings]

1 to 4 are flow sheets showing an outline of the method for treating wastewater from a methacrylic acid production plant according to the present invention, and
FIG. 5 is a flow sheet showing an outline of the method for producing methacrylic acid according to the present invention. 1.21a, 21b, 49.61 ... reactor, 13
．． 33,53.73...Wastewater supply line, 14.19
．． 20, 24.34.39, 40.59.74.79.
80...Air supply line, 121...Methacrylic acid condensation column, 122...Extraction column, 123...Solvent recovery column.

Claims (12)

[Claims] (1) Wastewater from a methacrylic acid production plant containing acetic acid and aldehydes is heated to 370°C or less using a wet oxidation reactor filled with a solid catalyst and under a pressure that maintains the liquid phase in the wastewater. A method for treating wastewater from a methacrylic acid manufacturing plant, comprising wet oxidizing organic substances in a gas containing molecular oxygen. (2) The method for treating wastewater from a methacrylic acid production plant according to claim 1, wherein the solid catalyst is a catalyst whose carrier component is an oxide containing titanium. (3) The solid catalyst is a carrier composed of an oxide containing titanium, and a compound of at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, cerium, and silver, or platinum. , Valadium,
A catalytically active component made of at least one metal selected from the group consisting of rhodium, ruthenium, and iridium is supported at a ratio of 25 to 0.05% by weight of the catalytically active component to 75 to 99.95% by weight of the carrier. The method for treating wastewater from a methacrylic acid manufacturing plant according to claim 2. (4) In the solid catalyst, the catalytic active component is at least one metal selected from the group consisting of platinum, rhodium, ruthenium, and palladium, and the metal is present in 0.1% of the total catalyst.
The method for treating wastewater from a methacrylic acid production plant according to claim 3, wherein the amount is 5% by weight. (5) The method for treating wastewater from a methacrylic acid production plant according to claim 1, wherein the wet oxidation reactor filled with a solid catalyst has a heat exchange function. (6) The method for treating wastewater from a methacrylic acid manufacturing plant according to claim 1, which comprises reusing the water to be treated after wet oxidizing the wastewater as plant water. (7) The method for treating wastewater from a methacrylic acid production plant according to claim 1, wherein the gas containing molecular oxygen is supplied at a linear velocity of the actual gas in the catalyst layer within a range of 0.6 to 20 cm/sec. (8) Methacrylic acid production plant wastewater contains acetic acid 0.04~
The method for treating wastewater from a methacrylic acid production plant according to claim 1, wherein the wastewater contains 20% by weight and 0.02 to 4% by weight of aldehydes. (9) The methacrylic acid manufacturing plant wastewater according to claim 2, wherein the carrier containing an oxide containing titanium is one kind of oxide selected from the group consisting of titania, titania-silica, and titania-zirconia. Processing method. (10) The method for treating wastewater from a methacrylic acid production plant according to claim 9, wherein the oxide is a binary composite oxide comprising 20 to 90 mol% of titania and 80 to 10 mol% of zirconia. (11) At a position 30% from the inlet side of the catalyst layer, aldehydes in the methacrylic acid production plant wastewater are 50 to 1
The method for treating wastewater from a methacrylic acid production plant according to claim 1, wherein the wastewater is oxidized. (12) Acetic acid and Wastewater containing aldehydes is treated with molecular oxygen using a wet oxidation reactor packed with a solid catalyst at a temperature of 370°C or less and under a pressure that maintains the wastewater in a liquid phase. Purified by wet oxidation under the supply of gas containing
A method for producing methacrylic acid, which comprises circulating the thus purified wastewater to an oxidation product gas absorption step to absorb the oxidation product gas.